Abstract The specific activity of supported nickel for benzene hydrogenation, ethane and n-hexane hydrogenolysis decreases with the increasing acidity of the support in the order of SiO 2 > Al 2O 3 > silica-alumina > Y faujasite; the Y faujasites (Na, Li, Ca, Mg) all have the same activities. The reducibility of 3% nickel faujasites decreases from 100% to zero in the order NaY ~ LiY > CaY > MgY > NH 4Y = 0. Specific n-hexane isomerization rates increase with acidity so that isomer yields are maximized for CaY. There are two types of sites on nickel. Site I (35%) promotes hydrogenolysis, Site II (65% weaker than Site I) hydrogenation-dehydrogenation. There is no evidence for synergistic influences between metal and acid sites.